PROJECT SUMMARY/ABSTRACT: The U.S. health care system is undergoing a period of substantial consolidation. Hospitals are purchasing many physician practices and half of all physicians are now employed by hospitals or integrated delivery systems. Although vertical integration (e.g., consolidation of hospitals and physicians) could improve quality through care coordination, it could also reduce quality or increase unnecessary use and spending, and the evidence quantifying these effects is limited. Our long-term goal is to understand the role of provider consolidation in care quality and population health. Our objective is to examine colonoscopy use among GI practices as an illustrative scenario to evaluate the impact of hospital-specialist consolidation on the quality of care, health outcomes, and resource use. Our specific aims address the following questions: (Aim 1: Quality) To examine the impact of change in ownership status of GI practices and the colonoscopy quality of physicians and practices measured as: a) procedure quality (polypectomy rates, incompletion rates, and complication rates) b) patient management (screening colonoscopy rate, appropriateness of follow-up and surveillance intervals) and c) health outcome measures (interval cancer incidence). (Aim 2: Resource Use) To examine the association between the change in ownership status of GI practices and CRC resource use and spending. We will exploit a natural experiment in which Medicare reimbursement differences between hospital outpatient departments and physician practices created a strong financial incentive for hospitals to acquire practices. We will use causal inference methods such as inverse probability weighting and instrumental variables using state-level variations in the antitrust enforcement efforts to adjust for the differences among providers. Our contribution is significant since it will be the first evaluation of the effect of consolidation between hospitals and specialists on the quality of care, the area with currently limited evidence. Our study can also contribute to the clinical literature by examining the provider-level variation in important colonoscopy quality measures, which are predictors of cancer outcomes but currently have large amount of poorly understood variations. The proposed study is innovative because it uses data from nationally representative population linked to epidemiologic information to reduce biases and improve generalizability; uses finer measure of quality by focusing on a homogenous clinical area; and adapts a quasi-experimental design to address potential confounders and make strong causal claims.